Hi L,
The performance of an NVMe SSD will indeed vary depending on whether you connect it externally via USB or internally via a PCIe slot.
Internal installation: NVMe SSDs connected directly to the motherboard via PCIe are capable of reaching speeds up to 3,500 MB/s.
External installation (USB 3.1): Depends greatly on the specific USB port and controller but typically won't be able to take full advantage of the drive's potential speed. The maximum theoretical speed for USB 3.1 gen 2 is 1,250 MB/s but real-world speeds are often around the 800-1000 MB/s mark due to protocol overhead.
So, if maximum performance is your goal, you should ideally install the SSD directly on your motherboard using a PCIe slot, if one is available. This should unlock the full potential of your NVMe SSD, especially compared to connecting it through USB.
However, using it externally should still provide very good performance that could very well fulfill the demands of running virtual machines. It might also provide advantages in portability or cooling depending on your exact setup.
That being said, it's important to remember that disk speed is just one part of ensuring good performance for your virtual machines. You'll also need to allocate enough CPU and RAM resources to your VMs.
Ultimately, I'd suggest trying your SSD as an external drive first. If you're not satisfied with the performance, then consider installing it internally. This way, you'll have a better understanding of the real-world difference in performance between the two methods in your specific operating environment.
Cheers!